DIY 2Q power supply

[bdori]

Hi all,

I'm playing with the idea to build a 2 quadrant power supply, a DIY version of the R&S NGM202. So far this is the main circuit that I came up with:



Simulation:


This is just a concept of the voltage control, current limiter and amplifier. I plan to add isolated control with STM32G4 + 16bit DAC + 24bit ADC, some protection, more current measurement options, and a nice front panel using STM32U5 + 4.3inch IPS LCD, just like the original R&S device. (No fast measurement option though with FPGA  )

What do you think about the presented concept? Is there any idea how can I improve this design?

Disclaimer: Although I'm an EE I spent most of my time as a Software Developer, so this is only hobby for me.

[jbb]

I recall that David Erikson did something a bit similar (http://www.djerickson.com/ps-load/) which might be nice for a comparison.

What sort of V out and I out range were you looking for? Because the higher these are the more heat your power transistors need to deal with...

[bdori]

Thanks, jbb. I have seen the awesome project from Erikson. He targeted an SMU, I just wanted to build a power supply, but just for the sake of fun I try to make it two quadrant. Honestly I don't really have the need for that  .

My target is 20V/3A, just like the NGM202. I will double the output darlingtons and add forced air cooling, to be able to handle 60W continuously.

[bdori]

So far, I have changed the output current limiting circuit, to reference to ground to be able to limit sink also.



But, I'm struggling here a bit. If you look at the imeas it does not go below 2.5 (vref) in sink, but it should according to AD8410A. It can measure current bidirectional, but somehow it does not work. Is it something with the simulation or I do oversee something? No clue, please help me to spot the issue.



Other than that I'm happy with the result. The step response looks ok.



I'll definitely breadboard the circuit to see it in action.

[bdori]

Of course it is nothing wrong with the simulation, simply I missed the fact that the AD8410A can only go to -2V on the low side. I have changed the current sensing to a difference amplifier (AD8276) and that works very well.

[jbb]

Just an FYI: the link above was for David Erikson’s 2Q supply, not his (much more complicated) SMU